This invention relates generally to a temperature indicating arrangement, and more particularly to a temperature indicating arrangement for indicating that a product has reached a critical temperature.
Many electronic components are usually affected by harmful changes in temperature. For example, electronic memory devices are manufactured by thin film processes. These processes typically utilize temperature sensitive manufacturing. These manufacturing processes also involve the laying down of metal or organic material. Generally, once the metal or organic material has been laid, the memory device is no longer able to withstand temperatures above a critical temperature. When the temperature rises above a critical level, metal laid in the low temperature manufacturing process may melt, one or more thin layers may alter characteristics, different materials may inter-diffuse, and organic material may break down. If this damage goes undetected, the use of these components may lead to defective performance, which can be harmful. As a result, it has become necessary to monitor the environmental conditions in which such electronic instruments are used and stored.
One type of electronic memory device affected adversely by rising temperatures is the MRAM (Magnetic Random Access Memory) device. MRAM memory devices may exist as a single chip or may be packaged as a collection of chips. As such, this technology may be packaged inside a computer system or may be employed as a removable card such as a PCMCIA card. In the manufacture of these devices, low temperature assembly and low temperature processes must be used to prevent the MRAM device from being exposed to excessive temperatures. MRAMs typically include nickel iron magnets that are permanently magnetized in one direction, and if the temperature exceeds 200-250 degrees Celsius, the magnet will lose its permanent polarization and the data will be unreliable. Therefore these components should not be used if they are exposed to such critical temperatures. It is important for a user to know or to guarantee that this part has not experienced an over-temperature.
In general, devices that monitor the temperature of temperature sensitive elements are known. For example, U.S. Pat. No. 5,954,010 teaches a temperature-sensing device for permanently indicating when a product is exposed to critical temperatures. This patent teaches a temperature-indicating device that changes shape according to the temperature. The disclosure teaches the use of the temperature-indicating device for monitoring a battery. The disclosure also teaches the use of the temperature-indicating device for monitoring computers, electronics, and power systems.
A possible disadvantage of this invention is that the temperature-monitoring device cannot be physically attached to the product per se, but only to the package encasing the product. Therefore there is no option to directly attach to the product that is being monitored. Also, the temperature-indicating device is cumbersome and cannot be used with smaller components. Another possible disadvantage is that the temperature-monitoring device of U.S. Pat. No. 5,954,010 involves the use of mechanical elements that require precision among various cooperating elements in order to work properly.
Another known temperature monitoring device is disclosed in U.S. Pat. No. 4,459,046. This patent teaches a self-adhesive temperature indicator for indicating the temperature of a body. It is not known what types of bodies this indicator is most suitable for, however, generally it is known to use adhesive temperature indicators for monitoring temperatures. It is also known to use adhesive temperature indicators to monitor the temperature of personal computer board components in electronic circuits. However, it is not generally known to use adhesive indicators to monitor replaceable memory cards such as MRAM cards.
With respect to memory cards, it is known to use electronic systems to electronically monitor the temperature. These devices store the thermal data using electronic memory devices, which may involve the use of a display, such as an LED or LCD, to indicate the temperature history. One possible disadvantage of these electronic monitoring devices it that they tend to be expensive. Another disadvantage is that these monitoring devices cannot be easily attached and detached from the device that is being monitored. Also, these electronic monitoring devices do not operate independently of the device being monitored. For instance, U.S. Pat. No. 5,471,040 teaches a capacitive data card system that has a blow fuse that changes color when elevated beyond a particular temperature. The fuse is a part of the operating system, and therefore does operate independently.
In one respect, the invention is a temperature warning arrangement. The arrangement comprises a memory device and a temperature indicator. In this respect, the temperature indicator comprises a wax-based substance arranged in a pattern. The wax-based substance has a melting point at a predetermined temperature. Also, the wax-based substance is externally attached to the memory device. In this respect, the operation of the temperature indicator is independent of operation of the memory device.
In another respect, the invention is a temperature warning arrangement. The temperature warning arrangement comprises a memory device and a multi-layered structure. In this respect, the multi-layered structure comprises an adhesive paper backing and a patterned layer. The patterned layer has a pattern. Also in this respect, the patterned layer is on the adhesive paper backing. The temperature warning arrangement also includes a transparent temperature sensitive layer laid over the patterned layer so that the pattern is visible there through. The transparent temperature sensitive layer changes visible characteristics at the predetermined temperature such that at the predetermined temperature the temperature sensitive layer obscures the visibility of the pattern.
In another respect, the invention is a method of monitoring the thermal history of a memory device. In this respect the method comprises, providing, on the exterior of the memory device, a temperature indicator. The temperature indicator comprises a wax material, wherein the wax material melts at a predetermined temperature. The method of monitoring the thermal history of the memory device also includes the step of monitoring the temperature indicator to see if the wax material has melted.
In another respect, the invention is a temperature indicator for use with a temperature sensitive product. The indicator comprises a paper backing and a patterned layer having a pattern wherein the patterned layer is placed on the paper backing. The temperature indicator also includes a transparent layer laid over the patterned layer so that the pattern is visible through the transparent layer. In this respect, the transparent layer changes visible characteristics at a predetermined temperature so as to obscure the visibility of the pattern.
In comparison to known prior art, certain embodiments of the invention are capable of achieving certain advantages including some or all of the following. One advantage is the simplicity of the method for producing a less expensive temperature-monitoring device. Also the use of waxes for indicating critical temperatures is advantageous because it is inexpensive, readily available and easily manipulated. Another advantage is the flexibility of use offered by this temperature-monitoring device. Because of its unobtrusive size and its application with regular label paper, the temperature-monitoring device can be easily fixed to temperature sensitive components of all sizes. Additionally, the operation of the temperature-monitoring device is wholly independent of the operation of the temperature sensitive device, thereby simplifying the operation and also making it more reliable. These and other advantages will be apparent to those skilled in the art upon reading the following detailed description of preferred embodiments, with reference to the below listed drawings.